1. Field of the Invention
The present invention relates to a pulse transformer used for transmission of pulse signals through LAN cables or so, for example.
2. Description of the Related Art
When a device such as a personal computer is connected to a network such as a LAN and a telephone network, it is necessary to protect the device from the entry of Electrostatic Discharge (ESD) and high voltage via a cable. Thus, a pulse transformer is used in a connector that constitutes a connection point between the cable and the device.
Pulse transformers conventionally used are manufactured by winding a primary coil and a secondary coil around a donut magnetic core (toroidal core), and have a property of transmitting only an AC component (pulse) of voltage applied to the primary coil to the secondary coil. Since a DC component is not transmitted to the secondary coil, the pulse transformers are able to interrupt ESD and high voltage.
Instead of the toroidal cores, drum cores have been used due to demand for miniaturization and surface mount of the pulse transformers. Such a pulse transformer is referred to as a surface-mount pulse transformer, and Patent Document 1 discloses an example thereof.
By the way, Ethernet communication speed of networks has become popular from 10 Mbps (bit per second) of 10BASE-T to 100 Mbps of 100BASE-TX, which is 10 times faster than 10BASE-T, and 1 Gbps of 1000BASE-T is currently popular. Also, 10GBASE-T (10 gigabits Ethernet (10 GbE)) is newly standardized.
Thus, pulse transformers having a small insertion loss especially at high frequency are demanded. When an insertion loss is small, a signal attenuation amount is small. When an attenuation amount of a component of high frequency is small, high-speed data signals can be accurately transmitted to the long distance. However, it is difficult for the conventional pulse transformers to reduce insertion loss at high frequency especially with severe standards.
Patent Document 1: Japanese Patent Application Laid-open No. 2009-21558